The objective of this research program is to seek evidence for biochemical regulation of aqueous humor secretion by the ciliary epithelia. Our working hypothesis is that cyclic nucleotides in the ciliary epithelia cells regulate secretion by controlling a membrane phosphorprotein system responsible for solute permeability of epithelial cell plasma membranes; intracellular cyclic nucleotide levels are in turn regulated by changes in the activity of enzymes responsible for their synthesis and degradation.